This paper analyzes a Type U burst at 1.0 – 2.8 GHz which occurred between 12:36:26 – 12:36:32 UT on 1992 August 22, observed by Ondřejov Observatory, Czech Republic. This may be the first example of Type U bursts in the decimetric range, as far as we know. From analysis we came to the following conclusion: (1) The frequency drift rates of the ascending and descending branches are 1.25 and 0.225 GHz/s, respectively, and the velocities of the electron beam are 0.38 c and 0.26 c, respectively; (2) The burst decay of the ascending branch is larger than that of the descending branch; (3) The variations of the maximum frequencies of instantaneous spectra with time appear as from the highest (1.92 GHz) to the lowest (1.0 GHz), then toward higher frequency (1.53 GHz) (this is consistent with that predicted by plasma emission theory); (4) The bandwidths of the ascending branch are about twice that of the descending branch (this may be caused by the larger drift rates of the ascending branch); (5) The temperature of the coronal loop apex is 6.3 × 106 K; (6) The magnetic field at the top of the loop is greater than 9.2 G; (7) This U burst emission is plasma radiation at the second harmonic.

Abstract This paper describes the U-type burst observed by Ondřejov Observatory on 1992-08-22 in the 6-second period 12:36:26-32 UT. To our knowledge it is the first time that a U-type burst was detected in the frequency range 1.0–2.8 GHz. Our analysis leads to the following conclusions: 1) The drift rates of the ascending and descending branches are 1.25 and 0.225 GHz/s, corresponding to beam velocities of 0.38 and 0.26 c. 2) The decay time constant is greater in the ascending than descending branches. 3) The maximum frequency varied in time from 1.92 GHz to 1.0 GHz, then back to 1.5 GHz. 4) The ascending branch had a band width about twice that of the descending branch. This may be related to its greater drift rate. The velocity dispersion Δν ν is estimated to be 0.42 for the ascending, and 0.47 for the descending branch.

太阳射电反转U型爆发,因它在频谱仪上的观测形态象反转过来的U而得名。它对研究太阳耀斑的物质抛射和粒子加速有重要意义。迄今为止,U型爆发绝大多数在低于0.5GHz的频率上出现,在1.1～1.7GHz上只报道了一例。本文中将介绍的在1.0～2.8GHz上的U型爆（见图1和图2）,在国际上尚属首例。这是由捷克Ondrejov天文台观测的,时间分辨率可达1ms,频率分辨率为10MHz。

The solar radio inverted-U bursts are named after their shape of an inverted letter Uon the spectrograph records.They are important in the study of the corona mass ejectionand particle acceleration in solar flares.Up to now,most U bursts occur at frequenciesbelow 0.5 GHz;only one exception was reported in the 1.1—1.7 GHz frequency band.Inthis note,we investigate a U burst in the 1.0-2.8 GHz frequency band(figs.1,2),

The new 100–4200 MHz Ondřejov radiospectrograph and the high-time resolution 3 GHz radiometer are described and the observations of fast drift bursts during the increased solar activity of September 5–7, 1992 are presented and analyzed.

Solar radio spectra in the range of 2.0-4.5 GHz observed by using a digital radio spectrometer at the Astronomical Observatory Ondrejov are presented. A brief description of the observational equipment and examples of solar radio spectra observed in the period April 10 - December 29, 1989 are given. The correlation of Fast Drift Bursts (FDB) and Type III bursts is presented.

Basing on radio measurements from different stations the paper presents a compilation of observations and resultinng questions concerning the interpretation of some remarkable features of the solar behind-limb event on 16th February 1984. The event was related to a very strong relativistic particle emission. Attention is paid to the related microwave radiation stimulating a discussion of the discrimination between plasma and gyromagnetic radiation being important for plasma diagnostics. Another outstanding feature is the occurrence of a spectacular multi-band U-shaped type II burst pattern challenging a discussion of possible higher harmonic plasma radiation.

Comparaison des mesures du continuum radio entre 100 et 1000 MHz avec le flux RX dans la region 2-320 keV

Calcul de la dependance radiale du champ magnetique coronal au-dessus de regions actives, en utilisant les donnees existant sur les sursauts de type I

Spectre dynamique des emissions radio entre 1000 et 45 MHz de frequence, enregistrements de sursauts a des frequences fixes et observations d'emissions RX a partir du satellite Prognoz 8, lors de la grande eruption chromospherique du 16 mai 1981

We present the main results obtained from the coordinated observations of solar radio noise storms organized by C.E.S.R.A. in May 1981. They concern the structure and polarization of radio sources, and the relation with the photospheric magnetic field. A model of coronal magnetic field, accounting for the observations, is briefly discussed.